The present invention relates to a method of controllably driving optics of a copier in the form of a scanner which is movable relative to an original document being laid on a glass platen.
In a copier of the type described, a scanner is driven at a predetermined speed during a scanning movement and at a higher speed during a returning movement. Especially, with a modern high-speed copier, high CPM (Count Per Minute) operations have to be implemented by reducing the period of time necessary for the return of the scanner which does not contribute to image forming at all. More specifically, while the rate of a scanning movement of the scanner is severely restricted for copying process reasons, the rate of a returning movement is free from this kind of restriction and, therefore, allows the returning time to be reduced for high CPM operations. It is a common practice to effect such returning movements at a high speed with no regard to the copy mode. As regards the high-speed returning movements, the position where the scanner should be brought to a stop in the vicinity of a home position thereof often fluctuates due to the fluctuation in the inertia and other factors of the optics and other similar loads. This does not matter at all during an ordinary copy mode operation, because the timing for feeding a paper sheet from a paper cassette can be controlled.
However, assume a two-sided copy mode or a composite copy mode in which two one-sided documents of format A4 which are fed sideways, for example, are transported and illuminated one after the other to reproduce them side by side on a paper sheet of format A3 which is fed lengthwise. Then, image transfer is executed with each of the leading and trailing halves of the same paper sheet and, as regards the second image transfer (second page), the paper sheet is driven into the image forming station before the scanner starts forming an image. More specifically, when the scanner starts forming an image, the paper sheet carrying an image on the leading half thereof has already moved away from a paper register station to make contact with a photoconductive element. In this kind of copy mode, should the stop position of the scanner fluctuate due to the high-speed return, the position for starting driving the scanner would also fluctuate resulting in the leading edge of an image fluctuating on the paper sheet.